1. Field of the Invention
The present invention relates to the technical field of touch control and, more particularly, to a touch sensing method and system for avoiding display noises.
2. Description of Related Art
The principle of a touch panel is based on different sensing manners to detect voltage, current, acoustic wave, or infrared for determining the coordinate of a touch point on a screen as touched by a finger or other medium such as stylus. For example, the resistive touch sensing technology makes use of a voltage difference between an upper electrode and a lower electrode to calculate the position of a point being pressed so as to detect the position of the touch point, and the capacitive touch sensing technology makes use of a capacitance change generated from static electricity combined between the arranged transparent electrodes and the finger of a human body so as to generate a current or voltage for determining the coordinate of the touching point. Therefore, with the capacitive touch sensing, a miniature capacitance change is employed to detect whether there are one or more touch points existed.
The capacitive touch sensing technology is to detect a capacitance change generated when a finger touches a touch panel so as to determine whether there is a touch occurred. FIG. 1 is a schematic diagram of a capacitive touch sensing technology. As shown in FIG. 1, in case of no noise interference, a sensing capacitance Cp is generated between the finger and the sense electrode 110, and the capacitance change of the sensing capacitance Cp is measured by a sensing circuit 120 so as to obtain data of the touch position. However, the capacitance change of the sensing capacitance Cp is very weak and thus is susceptible to noises, resulting in an erroneous measurement. Therefore, when a touch panel is attached onto a liquid crystal display (LCD) panel, the touch panel is susceptible to noises generated by the display panel.
The typical capacitive touch system has to measure the capacitance change on the touch panel by the sensing circuit so as to obtain data of touch position thereby calculating the coordinate of each position touched by the user. However, in the process of obtaining the touch data, the touch data is likely to shift or distort due to the noise interference in the sensing circuit, the touch panel, or even the driving circuit, the interference caused by external noise to ground, and the noise interference in the display panel or inside integrated circuits. It results in appearance of noise points as shown in FIG. 2, disappearance of the actual touch points, or coordinate offset. FIG. 2 schematically illustrates a touch sensing result with noise interference. As shown in FIG. 2, the real touch position is at the intersection of D6 and S1, however, the capacitive touch system would also report the intersection of D2 and S1 and the intersection of D2 and S3 as touch positions due to the noise interference. An erroneous measurement of the touch position occurs.
The noise interference from the display panel is usually unavoidable when the touch position is detected. When it occurs, the erroneous touch data is likely to be detected. To eliminate the affection of noise interference from the display panel, various methods have been developed.
In general, this problem can be solved directly by inserting one isolation layer between the touch panel and the display panel. FIG. 3 illustrates the aforementioned solution for noise reduction. As shown in FIG. 3, there is an electric field shielding layer 330 between a touch sensing layer 310 and a liquid crystal layer 320 for isolating the noises generated when a liquid crystal driving electrode layer 340 drives the liquid crystal layer 320, so as to avoid the touch sensing layer 310 from being interfered by the noises. There are disadvantages in this solution, unable to lower the manufacturing cost and restriction on the configuration for instance. FIG. 4 schematically illustrates the configuration of an embodiment using the electric field shielding layer 330. As shown in FIG. 4, due to the electric field shielding layer 330, the whole thickness of the touch display system is increased as well as the thickness of end product, resulting in a negative influence to the portability of the compact electronic products. In addition, in an in-cell or on-cell touch display panel, the touch components are arranged inside the display panel, and thus it is unable to insert the electric field shielding layer 330 into the display panel, so that the noises cannot be isolated by using the electric field shielding layer 330.
FIG. 5 schematically illustrates another solution by using an air gap to isolate noises and this solution is provided by Maxim, a touch IC manufacturer. As shown in FIG. 5, a gasket 510 is provided between an X-direction touch sensor and a display module to form an air gap for isolating the noises generated by the display module. However, the aforementioned problem cannot be eliminated by this solution.
To overcome the problem, a non-air-gap technique is proposed. The non-air-gap is to adhere an external glass (or a touch panel) directly to the display panel by a glue. Due to a vacuum formed between the glass and the display panel, the noises do not affect the operations of the touch panel. However, the yield of this technique is poor because a full adhesion between the display panel and touch panel is required, and the adhesion is getting more and more difficult as size of the display panel is increased. It would cause a huge loss when the adhesion fails. In addition, for an in-cell capacitive touch sensing, this method cannot be used because the typical in-cell capacitive touching sensors are arranged in the liquid crystal layer. As a result, in order to avoid damaging the feature of the liquid crystal display panel, this technique cannot be adopted.
In addition, it is applicable to use a filter to filter out the noises. Such a way is suitable for various touch panels, but it requires a noise simulation, which inevitably spends a lot of time on development of the filter and to increase the manufacturing cost of integrated circuits.
There is another method proposed to suppress the display noises by enlarging the voltage to increase signal to noise ratio (SNR). Although such a method surely can increase the accuracy of touch sensing, it is unable to effectively suppress the noises.
For the requirement on marketing, in addition to the function of touch sensing, a portable device also has to be provided with the function of hovering touch. FIG. 6 is a schematic diagram of a typical hovering touch. As shown in FIG. 6, the hovering touch requires accurately detecting the position of a finger on a touch panel when the finger is placed over, but not contacting, the touch panel. At this moment, the amount of capacitance change of the capacitance Cp generated by the finger being approached to the touch panel becomes extremely weaker, and thus the touch sensing is very difficult to perform if the level of the touch signal sensed by the sensing circuit is close to that of a noise. Namely, the hovering touch becomes more difficult if the display noise cannot be avoided.
For achieving the hovering touch, a typical in-cell configuration applied with an in-cell touch sensing is provided as shown in FIG. 7. Since the touch components are arranged inside the display panel, the touch sensing surely has to avoid the frame change time of the display panel, so as not to be affected by the display noise. Therefore, the display noise under this configuration can be eliminated theoretically. However, because the touch components have to be arranged inside the display panel, the yield is not improved yet.
Therefore, it is desirable to provide an improved touch sensing system and method to mitigate and/or obviate the aforementioned problems.